Low-cost digital television (“DTV”) receivers for hand-held devices use crystal oscillators as a clock source. The crystal oscillators are not temperature compensated. DTV receivers also use a demodulator chip that increases and decreases in temperature as the receiver receives video data in bursts, each burst of data representing one time slice during time slice mode of operation. The increase in temperature causes the crystal oscillator frequency to shift, or “drift,” in one direction, and the decrease in temperature causes the frequency to drift in the other direction.
FIG. 1 illustrates the drift using frequency offset updates, i.e., the difference of the frequency while receiving bursts and a reference frequency plotted over time. The drift illustrated in FIG. 1 is termed “short-term drift.” For example, note how the frequency drifts from −30 Hz to 0 Hz and drifts back to −30 Hz near the time of 1.1×104 ms in FIG. 1.
The short-term drift itself is subject to an overarching “long-term drift” as seen in FIG. 2, which illustrates frequency offsets over a longer period of time. For example, note how the short-term drift oscillations center around 0 Hz at 3×104 ms, but center around 40 Hz at 8×104 ms. Both short-term drift and long-term drift cause degraded performance in the DTV receiver. Also, the drifts can cause the DTV receiver to lose synchronization with the transmitter.